<form method="post" class="login-form">
    <table>
        <tr>
            <td class="label">用户名：</td>
            <td><input name="username" value="<?php echo $_POST['username']; ?>" required></td>
        </tr>
        <tr>
            <td class="label">密　码：</td>
            <td><input name="password" type="password" required></td>
        </tr>
    </table>
    <div style="text-align: center">
        <input type="submit" class="btn" value="登录">
    </div>
</form>